Retroreflective materials are employed for various safety and decorative purposes. Particularly, these materials are useful at night time when visibility is important under low light conditions.
Many types of retroreflective material exist for various purposes. These retroreflective materials can be used as reflective tapes and patches for clothing, such as vests and belts. Also, retroreflective bands can be used on posts, barrels, traffic cone collars, highway signs, warning reflectors, etc. Retroreflective material comprise arrays of randomly oriented micron diameter spheres or close packed cube-corner (prismatic) arrays.
A description of the structures and operation of cube-corner microprisms can be found in U.S. Pat. No. 3,684,348, issued to Rowland on Aug. 15, 1972, the teachings of which are incorporated by reference herein. A method for making retroreflective sheeting is also disclosed in U.S. Pat. No. 3,689,346, issued to Rowland (Sep. 5, 1972), the teachings of which are incorporated by reference herein. The disclosed method is for forming cube-corner microprisms in a cooperatively configured mold. The prisms are bonded to sheeting which is applied thereover to provide a composite structure in which the cube-corner formations project from one surface of the sheeting.
However, known retroreflective products have not been sufficiently supple and pliable to be worn for example, on clothing articles. Additionally, known retroreflective products have suffered from good launderability performance, which is becoming more desirable with the increased demand for clothing articles having retroreflective products thereon, such as running apparel and the like.
A retroreflective structure and method for forming the same are provided which includes a polyurethane sheet having a first side and a second side, a coating on the first side, and an array of retroreflective prism elements formed on the coating. Preferably, the polyurethane sheet has a thickness between about 25.4 and 127 micrometers (1 and 5 mils), and more preferably between about 50.8 and 76.2 micrometers (2 and 3 mils). In one embodiment, the array of retroreflective elements include cube-corner prism elements which have a window side and a facet side. Preferably, the window sides face the polyurethane sheet.
The coating can be used for purposes such as promoting adhesion between the prism elements and the first side of the polyurethane sheet. The coating can include a urethane coating which can also include a polyaziridine or isocyanate cross-linking agent. The coating can have a thickness in the range of between about 2.5 and 25 micrometers (0.1 and 1.0 mils). Preferably, the coating has a thickness in the range of between about 2.5 and 12.5 micrometers (0.1 and 0.5 mils).
A second coating can be formed on the second side of the polyurethane sheet for purposes such as forming a protective layer over the polyurethane sheet and can include ultraviolet blocking material. The coating can include a urethane coating which can also include a polyaziridine cross-linking agent. The coating can have a thickness in the range of between about 5 and 25 micrometers (0.2 and 1.0 mils). Preferably, the coating has a thickness in the range of between about 5.0 and 12.5 micrometers (0.2 and 0.5 mils).
In one embodiment, the array of retroreflective elements are cube-corner prisms. A reflective coating, such as a metallized coating, can be formed over the array of retroreflective elements. A backing layer can be provided over the array of retroreflective elements.
In high melt embodiments, a retroreflective structure is provided which includes a low melt temperature polyurethane sheet having a first side and a second side, a high melt temperature polyurethane sheet disposed on the first side of the low melt temperature polyurethane sheet, and an array of retroreflective prism elements disposed on the second side of the low melt temperature polyurethane sheet. The high melt temperature polyurethane sheet can include slip agents, such as a wax or metal soap.
The present invention has many advantages including being sufficiently thin to be flexible for placing on clothing. Further, the structure is sufficiently durable to withstand multiple washes.